Using differentiated reverse activity bits (RABs) based on mobile-station revision

ABSTRACT

Methods and systems are provided for improving reverse-link performance by using differentiated reverse activity bits (RABs) based on mobile-station revision. In an embodiment, an access node provides wireless service to first and second mutually exclusive sets of access terminals, the first operating according to IS-856, Release 0, the second according to IS-856, Revision A. The access node maintains first and second RAB thresholds, and periodically (a) measures reverse noise rise (RNR), (b) compares the RNR to the first and second thresholds, (c) transmits a first RAB to the first set of access terminals, and (d) transmits a second RAB to the second set of access terminals. The first RAB is set when the measured RNR exceeds the first threshold, and clear when it does not. The second RAB is set when the measured RNR exceeds the second RAB threshold, and clear when it does not.

BACKGROUND

1. Cellular Wireless Networks and EV-DO Generally

Many people use mobile stations, such as cell phones and personaldigital assistants (PDAs), to communicate with cellular wirelessnetworks. These mobile stations and networks typically communicate witheach other over a radio frequency (RF) air interface according to awireless communication protocol such as Code Division Multiple Access(CDMA), perhaps in conformance with one or more industry specificationssuch as IS-95 and IS-2000. Wireless networks that operate according tothese specifications are often referred to as “1xRTT networks” (or “1xnetworks” for short), which stands for “Single Carrier RadioTransmission Technology.” These networks typically provide communicationservices such as voice, Short Message Service (SMS) messaging, andpacket-data communication.

Mobile stations typically conduct these wireless communications with oneor more base transceiver stations (BTSs), each of which sendcommunications to and receive communications from mobile stations overthe air interface. Each BTS is in turn communicatively connected with anentity known as a base station controller (BSC), which (a) controls oneor more BTSs and (b) acts as a conduit between the BTS(s) and one ormore switches or gateways, such as a mobile switching center (MSC)and/or packet data serving node (PDSN), which may in turn interface withone or more signaling and/or transport networks.

As such, mobile stations can typically communicate with one or moreendpoints over the one or more signaling and/or transport networks frominside one or more coverage areas (such as cells and/or sectors) of oneor more BTSs, via the BTS(s), a BSC, and an MSC and/or PDSN. In typicalarrangements, MSCs interface with the public switched telephone network(PSTN), while PDSNs interface with one or more core packet-data networksand/or the Internet.

Recently, service providers have introduced mobile stations and wirelessnetworks that communicate using a CDMA protocol known as EV-DO, whichstands for “Evolution Data Optimized.” EV-DO networks, operating inconformance with one or more releases and/or revisions of industryspecification IS-856, such as Release 0 and Revision A, both of whichare hereby incorporated herein by reference, provide high ratepacket-data service (including Voice over IP (VoIP) service) to mobilestations using a combination of time-division multiplexing (TDM) on theforward link (from the network to mobile stations) and CDMA technologyon the reverse link (from mobile stations to the network). Furthermore,some “hybrid” mobile stations can communicate with both 1x networks andEV-DO networks.

In the EV-DO context, a mobile station is typically referred to as anaccess terminal, while the network entity with which the access terminalcommunicates over the air interface is known as an access node. Theaccess node typically includes a device known as a radio networkcontroller (RNC), which is similar to a BSC in 1x networks. The accessnode also includes one or more BTSs, each including one or more antennasthat radiate to define wireless coverage areas such as cells andsectors. Note that sectors are used in the balance of this writtendescription as an example of a wireless coverage area, though this isfor explanation and not to the exclusion of cells or other coverageareas. Among other functions, the RNC controls one or more BTSs, andacts as a conduit between the BTSs and a PDSN, which provides access toa packet-data network. Thus, when positioned in a sector provided by anaccess node, an access terminal may communicate over the packet-datanetwork via the access node and the PDSN.

2. Reverse Noise Rise

In general, in a given sector, an access node can provide service toaccess terminals on one carrier frequency (i.e. carrier), or on morethan one. Furthermore, interference can be, and often is, present on acarrier in a sector. As used herein, an instance of a given carrier in agiven sector may be referred to as a sector-carrier. In general, on asector-carrier, an access node receives transmissions from accessterminals operating on that sector-carrier. However, the access nodeoften also receives transmissions on that sector-carrier from otheraccess terminals, other devices, and/or any other sources ofinterference on that frequency.

At a given moment, the sum total of what an access node is receiving ona given sector-carrier is known as the reverse noise on thatsector-carrier. At regular intervals, and in fact quite frequently(e.g., once for every forward-link timeslot (i.e. once everyapproximately 1.67 ms)), access nodes compute reverse noise rise (RNR),which is the difference between (i) the reverse noise that the accessnode is currently detecting and (ii) a baseline level of reverse noise.Thus, the access node computes how far the reverse noise has risen abovethat baseline.

To determine the baseline, EV-DO networks typically periodically utilizewhat is known as a silent interval, which may occur on the order of onceevery five minutes, and last on the order of 40-100 ms, both of whichare typically configurable. During the silent interval, access terminalsknow not to transmit anything to the access node. The access node canthen measure whatever else is out there. As such, the baselinecorresponds to the amount of reverse noise when the sector-carrier isunloaded (i.e. without any transmitting access terminals). And otherreverse-link-noise levels, such as 24-hour or other minimums, could beused as a baseline.

In general, the lower the RNR is at a given moment, the more favorablethe RF conditions are for communication between access terminals and anaccess node at that moment. Correspondingly, the higher the RNR, theless favorable the RF conditions are. Moreover, a low RNR generallycorresponds to a sector-carrier being lightly loaded, in other wordsthat is supporting communications for a relatively low number of accessterminals. A high RNR, as one might expect, generally corresponds to asector-carrier being heavily loaded, in other words that is supportingcommunications for a relatively high number of access terminals.

3. Reverse Activity Bit (RAB)

Access nodes typically use the calculated value of RNR to, among otherthings, set or clear what is known as the Reverse Activity Bit (RAB),which is a value that the access node makes equal to 0 or 1, andrepeatedly transmits to all the access terminals operating on a givensector-carrier. Note that making the RAB equal to 0 is known as“clearing” the RAB, while making the RAB equal to 1 is known as“setting” the RAB. As stated, the access node typically calculates RNRat the same frequency at which it transmits forward-link timeslots, oronce every 1.67 ms. The access node typically sets or clears the RAB atthis same frequency.

With respect to how the access node chooses whether to set or clear theRAB, if the RNR is above a threshold (i.e. the “RNR threshold”), whichis a configurable parameter that may be between 0 dB and 30 dB, theaccess node sets the RAB. If the RNR is below the RNR threshold, theaccess node clears the RAB. The access node transmits the RAB in a TDMchannel—known as the reverse-activity channel—on the forward link. Thatchannel is itself a TDM portion of a forward-link channel known as theMedia Access Control (MAC) channel. Note that the RAB is the same forall access terminals on a sector-carrier. The manner in which thoseaccess terminals use the value of the RAB is explained below.

4. Access Terminals Using the RAB Under IS-856, Rel. 0

The initial release of IS-856 is referred to as Release 0 (Rel. 0),while a subsequent revision is referred to as Revision A (Rev. A). Thissubsection relates to how EV-DO access terminals use the RAB in EV-DOnetworks that operate according to Rel. 0, while the next subsectionrelates to how EV-DO access terminals use the RAB in EV-DO networks thatoperate according to Rev. A. Note that some EV-DO networks may provideboth Rel. 0 and Rev. A service; that is, a given EV-DO network mayprovide service to access terminals that operate according to Rel. 0,and also to access terminals that operate according to Rev. A.

Under Rel. 0, access terminals can transmit data to access nodes on thereverse link at five different data rates: 9.6 kilobits per second(kbps), 19.2 kbps, 38.4 kbps, 76.8 kbps, and 153.6 kbps. Transmission atthese various data rates involves using different types of coding forthe data to be transmitted, among other differences. Note that, during agiven instance of an access terminal transmitting data to an accessnode, the access terminal typically starts out using the lowest of thosedata rates, 9.6 kbps.

Recall that the EV-DO reverse link is essentially a CDMA channel overwhich the access terminal transmits data to the access node. And theaccess terminal does so in units of time known as frames, each of whichlast approximately 26.67 ms, which is the length of time of 16 timeslotson the forward link. And the network is synchronized on CDMA time, suchthat sets of 16 timeslots on the forward link will be aligned alongreverse-link-frame time boundaries.

So, the EV-DO access terminal will transmit its first frame to theaccess node at 9.6 kbps. And then, for the next frame, the accessterminal will stay at that rate, or perhaps transition up to 19.2 kbps.From there, frame by frame for all subsequent frames, the accessterminal will transmit at the rate that it is currently using,transition up to the next-higher rate, or transition down to thenext-lower rate. Note that rate-setting frequencies other than everyframe, such as every other frame or perhaps every four frames, could beused as well.

These (in this example) frame-by-frame decisions to maintain or changethe reverse-link data rate are controlled by the RAB and by a table ofreverse-link transitional probabilities that are stored by each accessterminal. This table is typically sent from the access node to theaccess terminal during the session-setup process, though it can also besent (or updated) as new air-interface connections are made between theaccess node and the access terminal, or perhaps periodically, or perhapsin response to some other event.

The table typically contains eight probabilities, each expressed as aninteger between 0 and 255, as explained more fully below. The eightprobabilities correspond to the eight possible transitions among thefive possible data rates. So, the transitional probabilities correspondto transitioning (in kbps) (1) from 9.6 up to 19.2, (2) from 19.2 up to38.4, (3) from 38.4 up to 76.8, (4) from 76.8 up to 153.6, (5) from153.6 down to 76.8, (6) from 76.8 down to 38.4, (7) from 38.4 down to19.2, and (8) from 19.2 down to 9.6.

Typically, when an access terminal is at the start of transmitting agiven frame at a given data rate (say, 38.4 kbps), the access terminalchecks the RAB. If the RAB is cleared (i.e. equal to 0), the RNR in thesector is not above the RNR threshold, and thus the access terminalknows that it has two options with respect to the next frame: stay at38.4 kbps or move up to 76.8 kbps. To determine which of those optionsthe access terminal will take for the next frame, the access terminalgenerates a random integer between 0 and 255, and compares that randominteger with the appropriate transitional probability. In this example,the access terminal would compare the random integer with the38.4-kbps-to-76.8-kbps value.

If the random integer is less than or equal to the38.4-kbps-to-76.8-kbps table value, the access terminal will transitionup to 76.8 kbps for the next frame. If not, the access terminal willstay at 38.4 kbps for the next frame. The table value is thus arepresentation of a probability, since the integer that the accessterminal compares with the table value is randomly generated. If, say,the table value were 255, the access terminal would have a probabilityof 1.00 (100%) for moving up to the next-higher data rate; if the tablevalue were 0, the access terminal would only have a 1/256 probability ofmoving up. And so on.

If the RAB is set (again, equal to 1), however, the access node hasdecided that there is too much reverse noise on the sector-carrier atthe moment, and thus the access terminal knows that it has two optionswith respect to the next frame. Again using 38.4 kbps as an example ofthe access terminal's current rate, the two options are to stay at 38.4kbps or move down to 19.2 kbps. To determine which of those options theaccess terminal will take for the next frame, the access terminal againgenerates a random integer between 0 and 255, and compares that randominteger with the appropriate reverse-link transitional probability. Thistime, the access terminal would compare the random integer with the38.4-kbps-to-19.2-kbps value.

As with transitions up to higher data rates, when talking abouttransitions down to lower data rates, the access terminal checks whetherthe random integer it generates is less than or equal to the38.4-to-19.2 table value. If so, the access terminal will transitiondown to 19.2 kbps for the next frame. If not, the access terminal willstay at 38.4 kbps for the next frame. Again, the table value representsa probability, as the integer that the access terminal compares with thetable value is randomly generated. If, the table value were 255, theaccess terminal would have a probability of 1.00 (100%) for moving downto the next-lower data rate; if the table value were 0, the accessterminal would only have a 1/256 probability of moving down. And so on.

5. Access Terminals Using the RAB Under IS-856, Rev. A

As explained above, under Rev. 0, reverse-link data rates are permittedonly to increase or decrease by one step at a time (i.e. up to thenext-higher data rate or down to the next-lower data rate), controlledby the RAB and the tables of reverse-link transitional probabilities.Under Rev. A, however, a more dynamic, iterative, equation-basedapproach is utilized, which permits data rates to change more rapidly.

Briefly, under Rev. A, the access node still repeatedly transmits a RABequal to 0 or 1. Each individual access terminal then uses that value tocompute what are known as a Quick Reverse Activity Bit (QRAB) and aFiltered Reverse Activity Bit (FRAB). The QRAB is binary (equal to 0 or1), while the FRAB is a real number having a value anywhere between −1and 1 inclusive. The QRAB is a short-term, binary indication of loading:a QRAB of 1 is associated with congestion on the sector-carrier, while aQRAB of 0 is associated with non-congestion. The FRAB is more of along-term, continuous, historical value, where values closer to −1indicate a lower degree of congestion on the sector-carrier reverselink, while values closer to 1 indicate a higher degree of congestion onthe sector-carrier reverse link. Thus, both the QRAB and the FRABreflect the access terminal's interpretation of the RAB from the accessnode.

The access terminal then calculates a value known in Rev. A as“T2PInflow.” T2PInflow is an iterative value: prior to each reverse-linktransmission, it has a current value, and that current value is one ofthe inputs in determining its value in the next calculation. Note thatthe “T2P” prefixes to many of the value and function names in thisexplanation means “Traffic to Pilot,” as one governing principle thatdrives the determination of reverse-link data rates under Rev. A is therelative values of (1) the power level that the access terminal is usingto transmit on the reverse-link portion of the traffic channel and (2)the power level at which the access terminal is detecting the pilotsignal from the access node, as is known in the art.

Rev. A defines two functions called “T2PDn(.)” and “T2PUp(.),” both ofwhich are functions of the current T2PInflow, FRAB, and a filtered valueof the serving sector pilot strength. If the access terminal sets QRABto 1 (corresponding to a relatively congested sector-carrier), thenT2PInflow will be decremented by the result of T2PDn(.); if, on theother hand, the access terminal sets QRAB to 0 (corresponding to arelatively non-congested sector-carrier), then T2PInflow will beincremented by the result of T2PUp(.). As with all of the details ofthese computations, the detailed equations can be found in IS-856, Rev.A.

Under Rev. A, this updated T2PInflow value is then used as one of theinputs in what is referred to as a “token bucket” mechanism, which isused to determine a packet size for the next reverse-link transmission.And it is this packet size that essentially determines the reverse-linkdata rate at which the access terminal will be transmitting, based on atable that correlates packet sizes to data rates. In general, higherreverse-link data rates are correlated with higher reverse-linktransmission power levels. In general, the token bucket mechanism isused as a regulator, to provide data-rate stability over time, whilestill permitting some instantaneous deviation.

One of the parameters of the token bucket mechanism is the“BucketLevel.” Using that value, the updated T2PInflow, and the FRAB,the access terminal calculates a value known as “PotentialT2POutflow.”The access terminal also maintains a data queue for outgoing data (i.e.data that is ready and waiting to be transmitted to the access node onthe reverse link). The access terminal keeps track of the current sizeof this data queue in a variable referred to here as the “data queuesize.” The access terminal determines the packet size for the nexttransmission based on PotentialT2POutflow, the data queue size, otherconstraints and maximum/minimum allowed values, and the accessterminal's transmission power.

As stated, the computed packet size essentially determines thereverse-link data rate. Under IS-856, Rev. A, effective reverse-linkdata rates can range from 19.2 kbps up to 1.84 megabits per second(Mbps). As a final part of the calculation, the access terminal computesa value known as “T2POutflow” (a.k.a. “actual T2POutflow”) based on thecomputed packet size. The access terminal then updates BucketLevel withthe updated T2PInflow value and the newly-calculated (actual) T2POutflowvalue, so that BucketLevel will be ready for the next iteration.

Overview

As explained, EV-DO access terminals use the value of the RAB indifferent ways under IS-856, Rel. 0 and IS-856, Rev. A for determiningtheir reverse-link data rates. However, under both standards, accessnodes make repeated, periodic broadcasts of the RAB (equal to 0 or 1) ona given sector-carrier, and all of the access terminals on thatsector-carrier, regardless of whether the access terminals are operatingaccording to IS-856, Rel. 0 or IS-856 Rev. A, interpret the RAB by (a)maintaining or increasing their reverse-link data rates when the RAB isclear and (b) maintaining or decreasing their reverse-link data rateswhen the RAB is set.

Access terminals operating according to IS-856, Rel. 0 (“Rel. 0 accessterminals”) have a maximum reverse-link burst rate of 153.6 kbps. Inother words, when Rel. 0 access terminals are transmitting reverse-linkdata, they can do so no faster than 153.6 kbps. Access terminalsoperating according to IS-856, Rev. A (“Rev. A access terminals”),however, have a maximum reverse-link burst rate of 1.8 Megabits persecond (Mbps). The conventional use of one RAB for all access terminals,Rel. 0 and Rev. A alike, on a sector-carrier has at least oneundesirable consequence: when a sector-carrier is serving a mix of Rel.0 and Rev. A access terminals, the Rel. 0 access terminals contributereverse noise, which may trigger the setting of the RAB, which will holddown the reverse-link data rates of the Rev. A access terminals. Thus,Rev. A access terminals are not able to realize their full reverse-linkpotential, which negatively impacts the experience of users engaging incommunications with Rev. A access terminals.

In accordance with the present methods and systems, an access nodemaintains separate RAB-triggering RNR thresholds (i.e. RAB thresholds)for Rel. 0 access terminals and for Rev. A access terminals (a “Rel. 0RAB threshold” and a “Rev. A RAB threshold”). The access nodecorrespondingly sends out two different RABs: one for Rel. 0 accessterminals (the “Rel. 0 RAB”) and the other for Rev. A access terminals(the “Rev. A RAB”), where the set or clear state of each RAB iscontrolled by the respective RAB threshold corresponding to that RAB. Inoperation, then, an access node periodically (and, as described, quitefrequently) (a) compares its most recent measurement of RNR to the Rel.0 RAB threshold, and responsively sets or clears the Rel. 0 RABaccordingly and (b) compares its most recent measurement of RNR to theRev. A RAB threshold, and responsively sets or clears the Rev. A RABaccordingly.

Further in accordance with the present methods and systems, Rel. 0access terminals monitor forward-link transmissions from the access nodefor the state of the Rel. 0 RAB, and then process the Rel. 0 RAB asdescribed above with respect to Rel. 0 access terminals processing theset or clear state of the RAB. Additionally, Rev. A access terminalsmonitor forward-link transmissions from the access node for the state ofthe Rev. A RAB, and then process the Rev. A RAB as described above withrespect to Rev. A access terminals processing the set or clear state ofthe RAB. In an embodiment, the access node transmits the Rel. 0 RAB inMAC sub-channel 0, and Rel. 0 access terminals monitor that sub-channelfor the state of the Rel. 0 RAB; further to this embodiment, the accessnode transmits the Rev. A RAB in MAC sub-channel 1, and Rev. A accessterminals that sub-channel for the state of the Rev. A RAB.

In an embodiment, the access node from time to time dynamically changesthe value of the Rel. 0 RAB threshold and the Rev. A RAB threshold for agiven sector-carrier based on the relative mixture of Rel. 0 accessterminals and Rev. A access terminals on the sector-carrier at the time.Thus, the access node may compute a ratio (which may hereinafter bereferred to as the “Rel. 0 ratio”) of (a) Rel. 0 access terminals beingserved on the sector-carrier to (b) all access terminals being served onthe sector carrier. Instead or in addition, the access node may computea ratio (which may hereinafter be referred to as the “Rev. A ratio”) of(a) Rev. A access terminals being served on the sector-carrier to (b)all access terminals being served on the sector carrier. Of course,either or both of these ratios could be expressed as percentages,decimal numbers, etc. Thus, if there were 10 Rel. 0 access terminals and30 Rev. A access terminals on a given sector-carrier, the Rel. 0 ratiowould be 0.25, and the Rev. A ratio would be 0.75.

Upon computing the Rel. 0 ratio and/or the Rev. A ratio, the access nodeuses one or both of those values to determine values (until the nextiteration) for the Rel. 0 RAB threshold and the Rev. A RAB threshold. Inan embodiment, the access node computes the Rel. 0 ratio and then usesthat computed value as a key into a table of pairs of Rel. 0 RABthresholds and Rev. A RAB thresholds for various ranges of Rel. 0ratios. In another embodiment, the table may contain offsets (i.e.differentials, deltas, etc.) than can be added or subtracted torespective default Rel. 0 and Rev. A RAB-threshold values to arrive atoperational Rel. 0 and Rev. A RAB thresholds.

And other implementations are certainly possible as well, such ascomputing and using the Rev. A ratio instead of the Rel. 0 ratio as akey into a table of thresholds or offsets. In some embodiments, a Rel. 0offset and a Rev. A offset may be identified and then added to the samedefault RAB threshold. For example, a certain Rel. 0 ratio may correlatewith (a) adding a negative Rel. 0 offset (e.g. −2 dB) to a given defaultthreshold to arrive at an operational Rel. 0 RAB threshold and (b)adding a positive Rev. A offset (e.g. 2 dB) to the same defaultthreshold to arrive at an operational Rev. A RAB threshold. In someembodiments, the Rel. 0 and Rev. A RAB thresholds could be computedbased on at least one of the Rel. 0 ratio and the Rev. A ratio, withoutreference to a lookup table. In any event, the access node may thenprovide service using the computed operational Rel. 0 and Rev. A RABthresholds until the next iteration.

In general, a relatively high RAB threshold would correspond with a RABbeing clear the majority of the time, since it would require arelatively high level of RNR to exceed that RAB threshold in order toset the RAB; thus, a relatively high RAB threshold would allow forreverse-link data rates to ramp up to relatively high levels, improvinguser experience. And a relatively low RAB threshold would correspondwith a RAB being set the majority of the time, since it would requireonly a relatively low level of RNR to exceed that RAB threshold in orderto set the RAB; thus, a relatively low RAB threshold would tend to holddown reverse-link data rates at relatively low levels, perhaps causing aworse user experience.

Thus, in an embodiment, between Rel. 0 and Rev. A access terminals,whichever group is more well represented at a given time on a givensector-carrier will be favored with an increased RAB threshold, and thusincreased potential for higher reverse-link data rates, while the groupthat is less well represented will experience a decreased RAB threshold,and thus decreased potential for higher reverse-link data rates.

In one example, if the Rel. 0 ratio was greater than or equal to 0.20and less than 0.30, the access node may offset the Rel. 0 RAB thresholdfrom a default RAB threshold by −3 dB, and may offset the Rev. A RABthreshold from the same default RAB threshold by +3 dB. If, however, theRel. 0 ratio was greater than or equal to 0.70 and less than 0.80, theaccess node may do the opposite; that is, the access node may offset theRel. 0 RAB threshold from the default RAB threshold by +3 dB, and mayoffset the Rev. A RAB threshold from the same default RAB threshold by−3 dB. And clearly numerous other examples are possible as well.

Note that an access node may identify a given access terminal as a Rel.0 access terminal or Rev. A access terminal by an identifier known as aMAC ID that is assigned to each access terminal during session setup. Inone embodiment, MAC IDs 2-63 may be assigned to Rev. A access terminals,while MAC IDs 64-127 may be assigned to Rel. 0 access terminals. Asdescribed above, the access node may use MAC sub-channel 0 to transmitthe Rel. 0 RAB, and may use MAC sub-channel 1 to transmit the Rev. ARAB. And other arrangements are certainly possible, such as assigningdifferent ranges of MAC IDs to Rel. 0 and Rev. A access terminals, usingdifferent MAC sub-channels for the two RABs, reserving additional and/ordifferent MAC sub-channels for other administrative purposes, and/ormany other possibilities.

And it should be noted that the above overview is illustrative and notlimiting. That is, additional and/or different features may be presentin some embodiments of the present invention. It should be noted as wellthat any description of an access node and/or one or more accessterminals communicating according to EV-DO is by way of example, andthat any suitable modes (e.g. protocols) may be used instead, such asCDMA, iDEN, TDMA, AMPS, GSM, GPRS, UMTS, EDGE, WiMax (e.g. IEEE 802.16),LTE, microwave, satellite, MMDS, Wi-Fi (e.g. IEEE 802.11), Bluetooth,infrared, and/or any other now known or later developed.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments are described herein with reference to thefollowing drawings, wherein like numerals denote like entities.

FIG. 1 depicts a communication system, in accordance with exemplaryembodiments;

FIG. 2 depicts a flowchart of a method, in accordance with exemplaryembodiments.

DETAILED DESCRIPTION OF THE DRAWINGS 1. Exemplary Architecture

FIG. 1 is a simplified block diagram of a communication system, inaccordance with exemplary embodiments. It should be understood that thisand other arrangements described herein are set forth only as examples.Those skilled in the art will appreciate that other arrangements andelements (e.g., machines, interfaces, functions, orders, and groupingsof functions, etc.) can be used instead, and that some elements may beomitted altogether. Further, many of the elements described herein arefunctional entities that may be implemented as discrete or distributedcomponents or in conjunction with other components, and in any suitablecombination and location. Various functions described herein as beingperformed by one or more entities may be carried out by hardware,firmware, and/or software. Various functions may be carried out by aprocessor executing instructions stored in memory.

As shown in FIG. 1, a communication system 100 includes an accessterminal (AT) 102, an access node 105 (shown as comprising a BTS 103 andan RNC 104), a PDSN 106, a packet-data network (PDN) 108, a gateway 110,and a PDN 112. And additional entities not depicted could be present aswell. For example, there could be more than one access terminal incommunication with access node 105; also, there could be additionalentities in communication with PDN 108 and/or PDN 112. Also, there couldbe one or more routers, switches, other devices and/or networks makingup at least part of one or more of the communication links.

Access terminal 102 may be any device arranged to carry out theaccess-terminal functions described herein, and may include a userinterface, a wireless-communication interface, a processor, and datastorage comprising instructions executable by the processor for carryingout those access-terminal functions. The user interface may includebuttons, a touchscreen, a microphone, and/or any other elements forreceiving inputs from users, as well as a speaker, one or more displays,and/or any other elements for communicating outputs to users.

The wireless-communication interface may comprise an antenna and achipset for communicating with one or more base stations over an airinterface. As an example, the chipset could be one suitable for engagingin EV-DO communications, including IS-856, Rel. 0 and/or IS-856, Rev. Acommunications. The chipset or wireless-communication interface ingeneral may also be able to communicate with a 1xRTT CDMA network, aWi-Fi (IEEE 802.11) network, and/or one or more additional types ofwireless networks. The processor and data storage may be any suitablecomponents known to those of skill in the art. As examples, accessterminal 102 could be or include a cell phone, a PDA, a computer, alaptop computer, a hybrid IS-2000/IS-856 device, and/or a multi-modeWi-Fi/cellular device.

BTS 103 may be any one or any combination of network elements arrangedto carry out the BTS functions described herein, and may include acommunication interface, a processor, and data storage comprisinginstructions executable by the processor to carry out those BTSfunctions. The communication interface may include one or more antennasand chipsets or other components for providing one or more coverageareas such as cells or sectors according to a protocol such as CDMA,EV-DO, WiMax, or any other suitable protocol. The communicationinterface may also include a wired or wireless packet-data interface(which may be characterized as a backhaul connection), such as anEthernet interface, for communicating with RNC 104.

RNC 104 may be any one or any combination of network elements arrangedto carry out the RNC functions described herein. As such, RNC 104 mayinclude a communication interface, a processor, and data storagecomprising instructions executable by the processor to carry out thoseRNC functions. The communication interface may include a wired orwireless packet-data interface (which may be characterized as a backhaulconnection), such as an Ethernet interface, for communicating directlyor over one or more networks with PDSN 106. In general, RNC 104functions to control one or more BTSs, and to serve as a conduit betweenthe one or more BTSs and PDSN 106, enabling access terminals tocommunicate over PDN 108 and perhaps beyond.

Note that access node 105 may comprise BTS 103 and RNC 104, and maycomprise one or more additional BTSs as well. In general, access node105 provides wireless service to access terminals over an air interface,and uses a backhaul connection to provide transport service over PDN 108(or perhaps PDN 108 and PDN 112) to those access terminals.

PDSN 106 may be any networking server or other device arranged to carryout the PDSN functions described herein. PDSN 106 may include acommunication interface, a processor, and data storage comprisinginstructions executable by the processor for carrying out those PDSNfunctions. The communication interface may include a wired packet-datainterface such as an Ethernet interface for communicating with accessnode 105 and/or over PDN 108. Note that PDSN 106 may, instead or inaddition, comprise a wireless-communication interface for communicatingwith access node 105 and/or over PDN 108. Note also that PDSN 106 mayuse the same interface or separate interfaces for communicating withaccess node 105 and for communicating over PDN 108. PDSN 106 maygenerally function to provide access node 105 with access to PDN 108,and vice versa.

Each of PDN 108 and PDN 112 may include one or more wide area networks,one or more local area networks, one or more public networks such as theInternet, one or more private networks, one or more wired networks, oneor more wireless networks, and/or one or more networks of any othertype. Devices in communication with PDN 108 and/or PDN 112 may exchangedata using a packet-switched protocol such as IP, and may be identifiedby an address such as an IP address. In this example, PDN 108 is theservice provider's privately-operated IP network (where the serviceprovider may operate at least access node 105 and PDSN 106), while PDN112 is the Internet. However, this is for illustration and not by way oflimitation. In some embodiments, PDSN 106 may connect directly to theInternet, in which case PDN 108 and gateway 110 may not be necessary.And other configurations are certainly possible as well.

Gateway 110 may be any networking server or other device arranged tocarry out the gateway functions described herein. Thus, gateway 110 mayinclude a communication interface, a processor, and data storagecomprising instructions executable by the processor for carrying outthose gateway functions. The communication interface may include a wiredpacket-data interface, such as an Ethernet interface, for communicatingover PDN 108 and/or PDN 112. Note that gateway 110 may, instead or inaddition, comprise a wireless-communication interface for communicatingover PDN 108 and/or PDN 112. Gateway 110 may use the same interface orseparate interfaces for communicating over PDN 108 and/or PDN 112.Gateway 110 may generally function to provide PDN 108 and PDN 112 withconnectivity to each other.

2. Exemplary Operation

FIG. 2 depicts an exemplary method that may be carried out by an accessnode such as access node 105. And although method 200 is describedherein as being carried out by access node 105, this is not required; ingeneral, method 200 may be carried out by an access node, a BTS, an RNC,a PDSN, one or more other network entities, or some combination thereof.

At step 202, access node 105 provides wireless service to a plurality ofaccess terminals on a carrier (e.g. a sector-carrier) in a coverage area(e.g. a sector). The plurality of access terminals consists of a firstsubset and a second subset, where the first and second subsets aremutually exclusive. The first subset operates according to IS-856, Rel.0, and the second subset operates according to IS-856, Rev. A.

At step 204, access node 105 maintains a first (i.e. Rel. 0) RABthreshold and a second (i.e. Rev. A) RAB threshold. Step 204 maycomprise periodically selecting values for the first and second RABthresholds based on at least one of (1) a first ratio of (a) the numberof access terminals in the first subset to (b) a total number of accessterminals in the first and second subsets and (2) a second ratio of (a)the number of access terminals in the second subset to (b) the totalnumber of access terminals in the first and second subsets. In someembodiments, only the first ratio is used. In other embodiments, onlythe second ratio is used. In still other embodiments, both ratios areused. Note that computing one of the ratios essentially computes theother as well, as the first and second ratios will add up to 1.

In an embodiment, selecting values for the first and second RABthresholds involves using one or both of the first ratio and the secondratio as a key into a table, in order to identify in the table thevalues for the first and second RAB thresholds. Access node 105 wouldthen operate using those identified values. In an embodiment, theidentified values are correlated in the table with a range of ratiovalues, wherein the range includes the first or second ratio.

In an embodiment, selecting values for the first and second RABthresholds involves using one or both of the first ratio and the secondratio as a key into a table, in order to identify in the tablerespective offset values for the first and second RAB thresholds. Accessnode 105 may maintain first and second default RAB thresholds thatcorrespond to the first and second RAB thresholds. Note that the firstdefault RAB threshold may be either equal or not equal to the seconddefault RAB threshold.

As such, access node 105 may compute values for the first RAB thresholdand/or the second RAB threshold by adding a respective offset value to arespective default RAB threshold to compute a respective RAB thresholdto use in operation. Instead or in addition, access node 105 maysubtract a respective offset value from a respective default RABthreshold to compute a respective RAB threshold to use in operation. Andother examples are certainly possible as well.

At step 206, access node 105 periodically carries out a number ofsub-steps including (a) measuring RNR on the carrier, (b) comparing themeasured RNR to each of the first and second RAB thresholds, (c)transmitting a first RAB to the first subset of access terminals, and(d) transmitting a second RAB to the second subset of access terminals.Access node 105 sets the first RAB when the measured RNR exceeds thefirst RAB threshold, and clears the first RAB when the measured RNR doesnot exceed the first RAB threshold. Similarly, access node 105 sets thesecond RAB set when the measured RNR exceeds the second RAB threshold,and clears the second RAB clear when the measured RNR does not exceedthe second RAB threshold.

As stated above, in an embodiment, access node 105 may transmit thefirst RAB to the first subset of access terminals in a first MACsub-channel, and similarly may transmit the second RAB to the secondsubset of access terminals in a second MAC sub-channel different fromthe first. The access terminals in the first subset may monitor thefirst MAC sub-channel for the first RAB, and the access terminals in thesecond subset may monitor the second MAC sub-channel for the second RAB.As explained, a RAB being set causes an access terminal receiving thatRAB to maintain or decrease its reverse-link data rate, while the RABbeing clear causes the access terminal to maintain or increase itsreverse-link data rate.

3. Conclusion

Various exemplary embodiments have been described above. Those skilledin the art will understand, however, that changes and modifications maybe made to those examples without departing from the scope of theclaims.

1. A method comprising: an access node providing wireless service to aplurality of access terminals on a carrier in a coverage area, theplurality of access terminals consisting of a first subset and a secondsubset, the first and second subsets being mutually exclusive, the firstsubset operating according to IS-856, Release 0, and the second subsetoperating according to IS-856, Revision A; the access node maintaining afirst reverse activity bit (RAB) threshold and a second RAB threshold;and the access node periodically: measuring reverse noise rise (RNR) onthe carrier, comparing the measured RNR to each of the first and secondRAB thresholds, transmitting a first RAB to the first subset of accessterminals, wherein the first RAB is set when the measured RNR exceedsthe first RAB threshold, and wherein the first RAB is clear when themeasured RNR does not exceed the first RAB threshold, and transmitting asecond RAB to the second subset of access terminals, wherein the secondRAB is set when the measured RNR exceeds the second RAB threshold, andwherein the second RAB is clear when the measured RNR does not exceedthe second RAB threshold.
 2. The method of claim 1, wherein the coveragearea is a sector, and wherein the carrier is a sector-carrier.
 3. Themethod of claim 1, wherein maintaining the first RAB threshold and thesecond RAB threshold comprises periodically selecting values for thefirst and second RAB thresholds based on at least one of (1) a firstratio of (a) a number of access terminals in the first subset to (b) atotal number of access terminals in the first and second subsets and (2)a second ratio of (a) a number of access terminals in the second subsetto (b) the total number of access terminals in the first and secondsubsets.
 4. The method of claim 3, wherein maintaining the first RABthreshold and the second RAB threshold comprises periodically selectingvalues for the first and second RAB thresholds based on the first ratio.5. The method of claim 3, wherein maintaining the first RAB thresholdand the second RAB threshold comprises periodically selecting values forthe first and second RAB thresholds based on the second ratio.
 6. Themethod of claim 3, wherein selecting values for the first and second RABthresholds comprises using at least one of the first ratio and thesecond ratio as a key into a table, wherein the access node uses the atleast one ratio to identify in the table the values for the first andsecond RAB thresholds.
 7. The method of claim 6, wherein the identifiedvalues are correlated in the table with a range of ratio values, whereinthe range includes the first or second ratio.
 8. The method of claim 3,wherein selecting values for the first and second RAB thresholdscomprises using at least one of the first ratio and the second ratio asa key into a table, wherein the access node uses the at least one ratioto identify in the table respective offset values for the first andsecond RAB thresholds.
 9. The method of claim 8, further comprising theaccess node maintaining first and second default RAB thresholds, whereinselecting values for the first and second RAB thresholds comprises atleast one of (a) adding a respective offset value to a respectivedefault RAB threshold to compute a respective RAB threshold and (b)subtracting a respective offset value from a respective default RABthreshold to compute a respective RAB threshold.
 10. The method of claim9, wherein the first default RAB threshold is equal to the seconddefault RAB threshold.
 11. The method of claim 9, wherein the firstdefault RAB threshold is not equal to the second default RAB threshold.12. The method of claim 1, wherein transmitting the first RAB to thefirst subset of access terminals comprises transmitting the first RAB ina first MAC sub-channel, and wherein transmitting the second RAB to thesecond subset of access terminals comprises transmitting the second RABin a second MAC sub-channel different from the first MAC sub-channel,wherein the access terminals in the first subset monitor the first MACsub-channel for the first RAB, and wherein the access terminals in thesecond subset monitor the second MAC sub-channel for the second RAB. 13.The method of claim 1, wherein a given RAB being set causes a givenaccess terminal receiving the given RAB to maintain or decrease areverse-link data rate for the given access terminal, and wherein thegiven RAB being clear causes the given access terminal to maintain orincrease the reverse-link data rate for the given access terminal. 14.An access node comprising: a communication interface comprising awireless-communication interface; a processor; and data storagecomprising instructions executable by the processor for causing theaccess node to carry out functions including: providing wireless serviceto a plurality of access terminals on a carrier in a coverage area, theplurality of access terminals consisting of a first subset and a secondsubset, the first and second subsets being mutually exclusive, the firstsubset operating according to IS-856, Release 0, and the second subsetoperating according to IS-856, Revision A; maintaining a first reverseactivity bit (RAB) threshold and a second RAB threshold; andperiodically: measuring reverse noise rise (RNR) on the carrier,comparing the measured RNR to each of the first and second RABthresholds, transmitting a first RAB to the first subset of accessterminals, wherein the first RAB is set when the measured RNR exceedsthe first RAB threshold, and wherein the first RAB is clear when themeasured RNR does not exceed the first RAB threshold, and transmitting asecond RAB to the second subset of access terminals, wherein the secondRAB is set when the measured RNR exceeds the second RAB threshold, andwherein the second RAB is clear when the measured RNR does not exceedthe second RAB threshold.
 15. The access node of claim 14, wherein thecoverage area is a sector, and wherein the carrier is a sector-carrier.16. The access node of claim 14, wherein maintaining the first RABthreshold and the second RAB threshold comprises periodically selectingvalues for the first and second RAB thresholds based on at least one of(1) a first ratio of (a) a number of access terminals in the firstsubset to (b) a total number of access terminals in the first and secondsubsets and (2) a second ratio of (a) a number of access terminals inthe second subset to (b) the total number of access terminals in thefirst and second subsets.
 17. The access node of claim 16, whereinmaintaining the first RAB threshold and the second RAB thresholdcomprises periodically selecting values for the first and second RABthresholds based on the first ratio.
 18. The access node of claim 16,wherein maintaining the first RAB threshold and the second RAB thresholdcomprises periodically selecting values for the first and second RABthresholds based on the second ratio.
 19. The access node of claim 16,wherein selecting values for the first and second RAB thresholdscomprises using at least one of the first ratio and the second ratio asa key into a table, wherein the access node uses the at least one ratioto identify in the table the values for the first and second RABthresholds.
 20. The access node of claim 19, wherein the identifiedvalues are correlated in the table with a range of ratio values, whereinthe range includes the first or second ratio.
 21. The access node ofclaim 16, wherein selecting values for the first and second RABthresholds comprises using at least one of the first ratio and thesecond ratio as a key into a table, wherein the access node uses the atleast one ratio to identify in the table respective offset values forthe first and second RAB thresholds.
 22. The access node of claim 21,the data storage further comprising instructions for maintaining firstand second default RAB thresholds, wherein selecting values for thefirst and second RAB thresholds comprises at least one of (a) adding arespective offset value to a respective default RAB threshold to computea respective RAB threshold and (b) subtracting a respective offset valuefrom a respective default RAB threshold to compute a respective RABthreshold.
 23. The access node of claim 22, wherein the first defaultRAB threshold is equal to the second default RAB threshold.
 24. Theaccess node of claim 22, wherein the first default RAB threshold is notequal to the second default RAB threshold.
 25. The access node of claim14, wherein transmitting the first RAB to the first subset of accessterminals comprises transmitting the first RAB in a first MACsub-channel, and wherein transmitting the second RAB to the secondsubset of access terminals comprises transmitting the second RAB in asecond MAC sub-channel different from the first MAC sub-channel, whereinthe access terminals in the first subset monitor the first MACsub-channel for the first RAB, and wherein the access terminals in thesecond subset monitor the second MAC sub-channel for the second RAB.